Sulfurized polybenzoxazine that can be used for coating metal and for the bonding of same to rubber

ABSTRACT

A polybenzoxazine sulfide has repeating units including at least one unit corresponding to formula (I) or (II):in which the two oxazine rings are connected together via a central aromatic group, the benzene ring of which bears one, two, three or four groups of formula —Sx—R in which “x” is an integer from 1 to 8 and R represents hydrogen or a hydrocarbon-based group including 1 to 10 carbon atoms and optionally a heteroatom chosen from O, S, N and P. Such a polybenzoxazine can be used as an adhesive layer on metal, in particular for the adhesive bonding of a metallic substrate, in particular made of carbon steel, to rubber.

1. FIELD OF THE INVENTION

The present invention relates to thermosetting resins, which may be usednotably in adhesive systems intended in particular for the adhesivebonding of metal to rubber.

The invention relates more particularly to polymers with benzoxazineunits or “polybenzoxazines” that may be used in particular as adhesivelayers in metal/rubber composites intended for the manufacture of rubberarticles such as pneumatic or non-pneumatic tyres, for motor vehicles.

2. PRIOR ART

Metal/rubber composites, in particular for motor vehicle tyres, are wellknown. They are usually composed of a matrix made of unsaturated rubber,generally diene rubber, which can be crosslinked with sulfur, includingmetal reinforcing elements (or “reinforcers”) such as yarns, films,tapes or cords made of carbon steel.

As they are subjected to very high stresses during the rolling of thetyres, notably to repeated actions of compression, bending or variationsin curvature, these composites must, in a known manner, satisfy a largenumber of sometimes contradictory technical criteria, such asuniformity, flexibility, flexural strength and compressive strength,tensile strength, wear resistance and corrosion resistance, and mustmaintain these performance qualities at a very high level for as long aspossible.

It is easily understood that the adhesive interphase between rubber andreinforcers plays a predominant role in the endurance of theseperformance qualities. The conventional process for connecting rubbercompositions to carbon steel consists in coating the surface of thesteel with brass (copper/zinc alloy), the bonding between the steel andthe rubber matrix being provided by sulfurization of the brass duringthe vulcanization or curing of the rubber. In order to improve theadhesion, use is generally made, in addition, in these rubbercompositions, of organic salts or metal complexes, such as cobalt salts,as adhesion-promoting additives.

However, it is known that the adhesion between the carbon steel and therubber matrix is liable to weaken over time as a result of the gradualdevelopment of the sulfides formed, under the effect of the variousstresses encountered, notably mechanical and/or thermal stresses, itbeing possible for the above degradation process to be accelerated inthe presence of moisture. Moreover, the use of cobalt salts renders therubber compositions more sensitive to oxidation and to ageing, andsignificantly increases the cost thereof, not to mention that it isdesirable to eliminate, in the long run, the use of such cobalt salts inrubber compositions due to the recent change in European regulationsrelating to metal salts of this type.

For all the reasons set out above, manufacturers of metal/rubbercomposites, in particular motor vehicle tyre manufacturers, are seekingnovel adhesive solutions in order to adhesively bond metal reinforcersto rubber compositions, while overcoming, at least in part, theabovementioned drawbacks.

Thus, the recently published patent applications WO 2014/063963, WO2014/063968, WO 2014/173838 and WO 2014/173839, filed by the ApplicantCompanies, have described novel polymers bearing urea, urethane orthiourea units, and also their starting monomers, which meet the aboveobjectives. Used notably as adhesion primer on metal in metal/rubbercomposites, these polymers make it possible very advantageously toadhesively bond the metal to the rubber matrices by subsequently usingsimple textile adhesives, such as “RFL” (resorcinol/formaldehyde latex)adhesives or other equivalent adhesive compositions, or else directly(that is to say, without employing such adhesives) to these rubbermatrices when the latter contain, for example, appropriatefunctionalized unsaturated elastomers, such as epoxidized elastomers.Thus, the cobalt salts (or other metal salts) can notably be left out ofthe rubber compositions intended to be connected to brass-coated metalreinforcers.

In continuing their research, the Applicant Companies have found a novelpolymer, of thermosetting type, which at room temperature has the sameadhesive performance, with respect to metal and rubber, as theabovementioned polymers, but which has, once thermoset (crosslinked),further improved thermal and chemical stability. Moreover, its specificmicrostructure makes it possible very advantageously to adjust theflexibility of the molecule depending on the particular applicationstargeted.

3. SUMMARY OF THE INVENTION

The present invention relates to a polybenzoxazine sulfide whoserepeating units include at least one unit corresponding to formula (I)or (II):

in which the two oxazine rings are connected together via a centralaromatic group, the benzene ring of which bears one, two, three or fourgroups of formula —S_(x)—R in which “x” is an integer from 1 to 8 and Rrepresents hydrogen or a hydrocarbon-based group including 1 to 10carbon atoms and optionally a heteroatom chosen from O, S, N and P.

The invention also relates to the use of such a polybenzoxazine aspolymeric coating of a substrate, at least the surface of which is atleast partly metallic, in particular for the adhesive bonding of such asubstrate to rubber.

The invention also relates to any substrate, at least the surface ofwhich is at least partly metallic, at least said metallic part beingcoated with the polymer according to the invention.

4. BRIEF DESCRIPTION OF THE FIGURES

The invention and the advantages thereof will be easily understood inthe light of the detailed description and the implementation exampleswhich follow, and also of FIGS. 1 to 11 which represent or depict:

-   -   the general principle for the synthesis of a benzoxazine        compound starting from three compounds, phenol, formaldehyde and        amine (R=residue of the amine) (FIG. 1 a );    -   the (ring-opening) mechanism for opening, by heat input, the        oxazine ring of such a benzoxazine compound (FIG. 1 b );    -   a general scheme for the synthesis, starting from a specific        phenol (the symbol “G” will be described in detail later),        paraformaldehyde and a specific aromatic diamine sulfide, of a        benzoxazine of formula (A-0) (Monomer denoted by “M-0”) that can        be used for the synthesis of a polybenzoxazine sulfide in        accordance with the invention (FIG. 2 );    -   a possible scheme for the synthesis, starting from a halogenated        phenol (the symbol “Hal” representing a halogen), p-formaldehyde        and the preceding specific aromatic diamine sulfide, of a        particular halogenated benzoxazine of formula (A-1) (Monomer        denoted by M-1) that can be used for the synthesis of a        polybenzoxazine in accordance with the invention (FIG. 3 );    -   another possible scheme for the synthesis, starting from another        specific phenol (the symbol “A” will be described in detail        later), p-formaldehyde and the preceding specific aromatic        diamine sulfide, of another benzoxazine of formula (A-2)        (Monomer denoted by M-2) that can be used for the synthesis of a        polybenzoxazine in accordance with the invention (FIG. 4 );    -   another possible scheme for the synthesis, starting from a        halogenated phenol, p-formaldehyde and a particular example of        an aromatic diamine sulfide, of another example of a particular        halogenated benzoxazine of formula (A-3) (Monomer denoted by        M-3) that can be used for the synthesis of a polybenzoxazine in        accordance with the invention (FIG. 5 );    -   another possible scheme for the synthesis, starting from another        specific phenol, p-formaldehyde and the preceding specific        example of an aromatic diamine sulfide, of another example of a        benzoxazine of formula (A-4) (Monomer denoted by M-4) that can        be used for the synthesis of a polybenzoxazine according to the        invention (FIG. 6 );    -   another possible scheme for the synthesis, starting from a        particular example of a phenol (Compound 1: methoxyphenol        bearing ethylenic unsaturation), p-formaldehyde (Compound 2) and        the preceding particular example (Compound 3) of an aromatic        diamine disulfide, of another example of a benzoxazine of        formula (A-5) (Monomer denoted by M-5) that can be used for the        synthesis of a polybenzoxazine sulfide according to the        invention (FIG. 7 );    -   a scheme for the general synthesis of an example of a        polybenzoxazine sulfide (Polymer denoted by P-1) according to        the invention, starting from the preceding halogenated        benzoxazine of formula (A-6) (Monomer M-6) and from another        monomer of general formula (B) (Monomer denoted by N) of the        aromatic diol or thiol type; and also this example of a        polybenzoxazine sulfide (Polymer denoted here by P-1′) according        to the invention once its oxazine rings have been opened after        heat treatment of the polymer P-1 (FIG. 8 );    -   a scheme for the synthesis of another polybenzoxazine according        to the invention (Polymer P-2′), with its oxazine rings opened,        obtained by homopolymerization of the preceding particular        halogenated benzoxazine of formula (A-5) (Monomer M-5) (FIG. 9        );    -   an example of synthesis, starting from brominated phenol        (compound 4), p-formaldehyde (compound 2) and a specific        aromatic diamine disulfide (compound 3), of a particular        brominated benzoxazine of formula (A-7) (Monomer denoted by M-7)        which may be used for the synthesis of polybenzoxazines (Polymer        P-3 and P-3′ of FIG. 11 ) in accordance with the invention (FIG.        10 );    -   finally, an example of synthesis of a polybenzoxazine sulfide        (Polymer by P-3) according to the invention, starting from the        preceding particular halogenated benzoxazine of formula (A-7)        (Monomer M-7) and from another particular monomer of formula        (B-1) (Monomer N-1) of the sulfur-based aromatic diol type        (bearing a thioether function), and also the structure of this        polymer once its oxazine rings have been opened (Polymer denoted        by P-3′) (FIG. 11 ).

5. DETAILED DESCRIPTION OF THE INVENTION

It will first of all be recalled that benzoxazines are compounds ofgeneral formula:

The appended FIG. 1 a recalls the general principle of the synthesis ofa benzoxazine, in this instance starting (condensation reaction) fromone molecule of phenol, from two molecules of formaldehyde and from anamine (R denoting the residue of the amine), with elimination of twomolecules of water.

FIG. 1 b for its part recalls the mechanism for opening the oxazine ring(ring-opening) of such a compound during a heat input (represented bythe symbol Δ).

Numerous benzoxazine compounds or monomers can thus be synthesized usingvarious phenols and amines according to their types of substituents.These substituting groups may subsequently provide polymerizable sitesand make possible the synthesis of various benzoxazine polymers (orpolybenzoxazines).

Benzoxazines and polybenzoxazines which result therefrom are productswhich are today well known to a person skilled in the art; to cite but afew publication examples, mention may be made of the papers“Polybenzoxazines—New high performance thermosetting resins: synthesisand properties”; N. N. Ghosh et al., Prog. Polym. Sci., 32 (2007),1344-1391, or “Recent Advancement on Polybenzoxazine—A Newly DevelopedHigh Performance Thermoset”, Y. Yaggi et al., J. Polym. Sci. Part A:Polym. Chem.: Vol. 47 (2009), 5565-5576, and also, for example, of thepatents or patent applications U.S. Pat. No. 5,543,516 and WO2013/148408.

As explained in detail in the above documents, polybenzoxazines have theremarkable ability, at high temperature (for example, typically greaterthan 150° C., or even greater than 200° C., depending on theirparticular microstructure), to open their oxazine rings and to thusresult in thermosetting polyphenol resin structures.

The specific polybenzoxazine that is the subject of the invention isderived from a benzoxazine (referred to as Monomer M in the presentapplication) of sulfide type which corresponds to the following genericformula (A):

in which formula (A) each benzene nucleus of the two oxazine rings bearsat least one (i.e. one or more) radical G; the benzoxazine itself thusbears at least two radicals G.

The (at least) two radicals G, which may be identical or different, arechosen from the group consisting of:

-   -   halogens;    -   groups —OR₁, —SR₁, —NR₂R₃; R₁, R₂ and R₃, which may be identical        or different, representing an alkyl containing 1 to 4 carbon        atoms; and    -   aliphatic hydrocarbon-based groups including 1 to 8 carbon        atoms, or cycloaliphatic hydrocarbon-based groups including 3 to        8 carbon atoms, or aromatic hydrocarbon-based groups including 6        to 12 carbon atoms; these saturated or ethylenically unsaturated        hydrocarbon-based groups also optionally including at least one        heteroatom chosen from O, S, N and P.

In this formula (A) as described previously for the polymer of theinvention, the two oxazine rings are connected together via a centralaromatic group, the benzene ring or nucleus of which (also referred toas the central benzene ring or nucleus) bears one, two, three or fourgroups of formula —S_(x)—R in which “x” is an integer from 1 to 8 and Rrepresents hydrogen or a hydrocarbon-based group including 1 to 10carbon atoms and optionally a heteroatom chosen from O (oxygen), S(sulfur), N (nitrogen) and P (phosphorus).

Similarly, it may be noted in this formula (A) that the two nitrogenatoms of the oxazine rings are, relative to each other, in any position(i.e. ortho, meta or para) on the central benzene nucleus. However,preferably, these two nitrogen atoms are in the meta-position relativeto each other; in other words, the starting benzoxazine (Monomer in thiscase denoted by M-0) from which is derived the polybenzoxazine of theinvention then preferentially corresponds to the generic formula (A-0)below:

The appended FIG. 2 gives the scheme for the general synthesis of thisbenzoxazinone of formula (A-0), with heat input and with elimination ofwater, starting from a specific phenol bearing at least one (i.e. one ormore) radical G, paraformaldehyde and, finally, a specific aromaticdiamine sulfide of formula:

in which formula, needless to say, the benzene ring bears one, two,three or four groups of formula —S_(x)—R as defined previously, and maybear other optional substituents (by way of example a methyl or ethylgroup).

Preferentially, in this benzoxazine of formula (A) or (A-0), the centralbenzene nucleus bears two groups of formula —S_(x)—R, these two groupsmore preferentially being in the meta-position relative to each other onthe benzene nucleus. According to another preferential embodiment, “x”is within a range from 1 to 4, more preferentially equal to 1 or 2. R ispreferentially an alkyl more preferentially containing 1 to 5 carbonatoms, even more preferentially a methyl or ethyl, in particular amethyl.

The polybenzoxazine of the invention (Polymer P), derived from thebenzoxazine of formula (A) described previously, thus has the essentialfeature of including structural repeating units including at least oneunit corresponding to formula (I) (before opening of the oxazine rings)or formula (II) (after ring opening) below:

The term “polymer” should be understood in the present patentapplication as meaning any homopolymer or copolymer, notably blockcopolymer, with repeating structural units including at least one unitof formula (I) or (II) above; needless to say, the polymer of theinvention may include both units of formula (I) and units of formula(II).

In formula (II) above, a person skilled in the art will immediatelyunderstand that the two symbols “*” (which may be identical ordifferent) represent any attachment of the unit to a carbon atom or to aheteroatom (preferably chosen from O, S, N and P), this attachment orbond resulting from the opening of the oxazine rings during a sufficientinput of heat (A).

In addition, in the above formulae (I) and (II), as for the monomer offormula (A), one or more hydrogen atoms of at least one or of eachbenzene nucleus of the two oxazine rings, and also those of the centralbenzene ring, may optionally also be substituted with varioussubstituents (by way of example a methyl or ethyl group), notably withfunctional groups (by way of example a vinyl group) capable of promotingthe adhesion of the polymer to the metal and/or to the rubber.

Similarly, as for the preceding monomer of formula (A), it may be notedin these formulae (I) and (II) that the two nitrogen atoms of theoxazine rings are, relative to each other, in any position (i.e. ortho,meta or para) on the central benzene nucleus which separates them.

However, preferably, these two nitrogen atoms are in the meta-positionrelative to each other on the central benzene nucleus; in other words,the polybenzoxazine of the invention then includes at least repeatingstructural units including (at least) one unit corresponding to formula(I-bis) (before opening of the oxazine rings) or formula (II-bis) (afteropening of the rings) below:

In the preceding formula (A) or (A-0), preferably, each benzene nucleusof the two oxazine rings bears only one radical G or at most two, morepreferentially only one radical G.

This radical (radical G) is even more preferentially located in the paraposition relative to the oxygen of the oxazine ring. In such a case, itwill be understood that the polybenzoxazine of the invention thus hasthe essential feature of including at least repeating structural unitsincluding (at least) one unit corresponding to formula (I-a) (beforeopening of the oxazine rings) or formula (II-a) (after ring opening)below:

Even more preferentially, “x” is equal to 1 and R represents a methyl.

Thus, as examples of aromatic diamine sulfides that are suitable for thesynthesis of a benzoxazine of formula (A) or (A-0) in which, accordingto a particularly preferential embodiment, “x” is equal to 1 and Rrepresents a methyl, mention will be made in particular of the compounds3,5-bis(methylthio)-2,4-toluenediamine,3,5-bis(methylthio)-2,6-toluenediamine and mixtures thereof,corresponding, respectively, to formulae (a) and (b) below:

In other words, according to a particularly preferential embodiment, ifthe benzoxazine of formula (A-0) is derived from at least one of theabove two isomers or from mixtures thereof, then the polybenzoxazine ofthe invention includes repeating units including at least one unitcorresponding to formula (I-a-1) or (I-b-1) (before opening of theoxazine rings), (II-a-1) or (II-b-1) (after ring opening) below:

According to a preferential embodiment, the (at least two) radicals G,which may be identical or different, represent a halogen such asbromine, chlorine, fluorine or iodine.

The appended FIG. 3 is a scheme of the general synthesis, with heatsupply and with elimination of water, starting from a halogenated phenolbearing at least one (i.e. one or more) halogen (represented by thesymbol “Hal”), p-formaldehyde and the specific aromatic diamine sulfideof the preceding FIG. 2 , of a particular halogenated benzoxazine offormula (A-1) (Monomer denoted by M-1) which may be used for thesynthesis of a polybenzoxazine in accordance with the invention. Thishalogen (Hal) is more preferentially bromine or chlorine, even morepreferentially bromine; the latter even more preferentially being in thepara position relative to the oxygen of each oxazine ring.

According to another preferential embodiment, the (at least two)radicals G, which may be identical or different, represent a groupchosen from —OR₁, —SR₁, —NR₂R₃; R₁, R₂ and R₃, which may be identical ordifferent, representing an alkyl containing 1 to 4 carbon atoms.

According to another preferential embodiment, the (at least two)radicals G, which may be identical or different, represent an aliphatichydrocarbon-based group (represented by the symbol “A”) including 1 to 8carbon atoms, or a cycloaliphatic hydrocarbon-based group including 3 to8 carbon atoms, or an aromatic hydrocarbon-based group including 6 to 12carbon atoms, this saturated or ethylenically unsaturatedhydrocarbon-based group “A” being able optionally to include a (at leastone) heteroatom chosen from O, S, N and P.

The appended FIG. 4 is a scheme of the general synthesis, with heatsupply and with elimination of water, starting from a halogenated phenolbearing at least one (i.e. one or more) such group “A”, paraformaldehydeand the specific aromatic diamine sulfide of the preceding FIGS. 2 and 3, of a particular benzoxazine of formula (A-2) (Monomer denoted by M-2)which may be used for the synthesis of a polybenzoxazine in accordancewith the invention.

FIG. 5 is another possible scheme for the synthesis, starting from ahalogenated phenol, paraformaldehyde and a specific example of anaromatic diamine disulfide, namely3,5-bis(methylthio)-2,6-toluenediamine of the preceding formula (b), ofanother example of a particular halogenated benzoxazine of formula (A-3)(Monomer denoted by M-3) that can be used for the synthesis of apolybenzoxazine in accordance with the invention.

FIG. 6 is another possible scheme for the synthesis, starting fromanother phenol (the symbol “A” has been described previously),paraformaldehyde and 3,5-bis(methylthio)-2,6-toluenediamine of thepreceding formula (b), of another example of a benzoxazine of formula(A-4) (Monomer denoted by M-4) that can be used for the synthesis of apolybenzoxazine according to the invention.

According to a preferential embodiment, the (at least two) groups “A”,which may be identical or different, represent an saturated orethylenically unsaturated aliphatic hydrocarbon-based group, including 1to 6 and in particular 1 to 4 carbon atoms, which may optionally includeat least one (i.e. one or more) heteroatom chosen from O, S, N and P.

Thus, according to another particular and preferential embodiment, thepolymer of the invention is derived from a benzoxazine disulfide whichcorresponds at least partly to one of the two formulae (A-5) and(A-5bis) (Monomers denoted, respectively, by M-5 and M-5bis) below:

FIG. 7 is a particular case of FIG. 6 which describes another scheme forthe synthesis, starting this time from a particular example of a phenol(Compound 1) corresponding to such a preferential definition (in thiscase, phenol bearing an ethylenic unsaturation and a methoxyl group),paraformaldehyde (Compound 2) and the particular example of thepreceding aromatic diamine disulfide (Compound 3), of another example ofa benzoxazine of formula (A-5) (Monomer denoted by M-5) which may beused for the synthesis of a polybenzoxazine sulfide according to theinvention.

A person skilled in the art is well aware of how to widely adaptspecific formula (A) or (A-0) of the benzoxazine serving as startingmonomer for the synthesis of the polybenzoxazine according to theinvention, by notably varying the formulae of the phenol (bearing theradical(s) G) and of the diamine sulfide (bearing the group(s) offormula —S_(x)R).

As examples of preferential aromatic diamine sulfides, mention hasalready notably been made of the compounds3,5-bis(methylthio)-2,4-toluenediamine,3,5-bis(methylthio)-2,6-toluenediamine, and mixtures thereof.

As examples of phenol compounds (in this case, for example,methoxyphenols) bearing groups “A” of the saturated or ethylenicallyunsaturated aliphatic hydrocarbon-based type, including 1 to 6 and inparticular 1 to 4 carbon atoms, which may optionally include at leastone (i.e. one or more) heteroatom chosen from O, S, N and P, examplesthat may be mentioned include the following compounds:

According to a preferential embodiment, the polybenzoxazine polymer ofthe invention may be obtained by polycondensation of a benzoxazine offormula (A) or (A-0) as described in detail previously, as firstmonomer, and, as second monomer, an aromatic diol or thiol compound.

This aromatic diol or thiol compound more preferentially corresponds toformula (B):HX₁—Ar₁—Z—Ar₂—X₂H  (B)in which:

-   -   X₁ and X₂, which may be identical or different, represent O or        S;    -   Ar₁ and Ar₂, which may be identical or different, represent an        aromatic group, preferably phenylene;    -   Z represents O or (S)_(n), the symbol “n” representing an        integer greater than or equal to 1.

Thus, according to one particularly preferred embodiment, thepolybenzoxazine of the invention is characterized by repeat unitsincluding at least one unit corresponding to the particular formulae(I-1) (before opening of the oxazine rings) or (II-1) (after ringopening):

In this case also, it is clearly noted that, in the above formulae, thetwo nitrogen atoms of the oxazine rings are, relative to each other, inany position (i.e. ortho, meta or para) on the central benzene nucleuswhich separates them.

However, even more preferentially, in the above formulae (I-1) and(II-1) above, these two nitrogen atoms are in the meta-position relativeto each other on the central benzene nucleus which separates them. Inother words, the polybenzoxazine of the invention then includesrepeating structural units including (at least) one unit correspondingto formula (I-1bis) (before opening of the oxazine rings) or formula(II-1bis) (after ring opening) below:

In the above formulae (I-1), (II-1), (I-1bis) and (II-1bis), one or morehydrogen atoms of at least one or of each aromatic nucleus Ar₁ and Ar₂could be substituted with various substituents, which may be identicalor different, for example functional groups capable of promoting theadhesion of the polymer to the metal and/or to the rubber.

FIG. 8 is a scheme for the general synthesis of a polybenzoxazinesulfide (Polymer denoted by P-1) according to the invention, of formula(I-1bis) above, starting from the preceding halogenated benzoxazine offormula (A-6) (Monomer M-6) and from another monomer of general formula(B) (Monomer denoted by “N”) of the aromatic diol or thiol type; andalso this example of a polybenzoxazine sulfide (Polymer denoted here byP-1′ of formula II-1bis) according to the invention once its oxazinerings have been opened after heat treatment of the polymer P-1.

In the general formulae (I-1), (II-1), (I-1bis) or (II-1bis) above,preferentially at least one of the following features is satisfied:

-   -   Ar₁ and Ar₂ each represent an unsubstituted phenylene group;    -   X₁ and X₂ each represent either a sulfur atom, or an oxygen        atom;    -   Z represents O or S (i.e. “n” equal to 1), more preferentially        S.

More preferentially, it is all of the preferential features above whichare simultaneously satisfied.

As preferential examples, the compound of the preceding formula (B)corresponds to at least one of the particular formulae (B-1), (B-2) or(B-3) below:

According to another particular and preferential embodiment, thepolybenzoxazine polymer of the invention may be obtained byhomopolymerization of a benzoxazine of formula (A) or (A-0) as describedabove.

Thus, FIG. 9 illustrates a scheme for the synthesis of anotherpolybenzoxazine according to the invention (Polymer P-2′ of formulaII-2), with its oxazine rings opened, this time obtained by simplehomopolymerization of the particular halogenated benzoxazine of thepreceding formula (A-5) (Monomer M-5).

According to another particular and preferential embodiment, the polymerof the invention is derived from a brominated benzoxazine polysulfidewhich corresponds at least partly to one of the two formulae (A-7) and(A-7bis) (Monomers denoted, respectively, by M-7 and M-7bis) below:

FIG. 10 precisely gives an example of synthesis, starting from thebrominated phenol (compound 4), p-formaldehyde (compound 2) and3,5-bis(methylthio)-2,6-toluenediamine (compound 3), of this brominatedbenzoxazine polysulfide of formula (A-7) (Monomer denoted by M-7) whichmay be used for the synthesis of polybenzoxazines (Polymer P-3 and P-3′of FIG. 11 ) in accordance with the invention.

In these examples of FIG. 10 , as for the preceding FIGS. 7 to 9 , it isnoted in particular, according to a particularly preferential embodimentof the invention already indicated, that each benzene nucleus of the twooxazine rings of the benzoxazine of formula (A) bears only one halogen(Hal), more preferentially bromine, located in the para positionrelative to the oxygen of the oxazine ring.

Finally, FIG. 11 describes the synthesis of a polybenzoxazine sulfide(Polymer P-3) according to the invention, starting from the particularhalogenated benzoxazine of formula (A-7) (Monomer M-7) above and fromanother particular monomer of formula (B-1) (Monomer N-1) of thesulfur-based aromatic diol type (bearing a thioether function), and alsothe structure of this polymer once its oxazine rings have been opened(Polymer denoted by P-3′).

The syntheses of FIGS. 10 and 11 will be described in greater detail inthe implementation examples that follow.

Typically, the polybenzoxazine of the invention may include from ten toseveral hundred, preferably from 50 to 300, structural units bearingunits of formula (I) and/or (II), in particular structural units asrepresented as examples in FIGS. 8, 9 and 11 .

The polybenzoxazine of the invention may advantageously be used, asadhesion primer or as sole adhesive layer, for coating a metalsubstrate, at the very least a substrate of which at least the surfaceis at least partly metallic, and notably making this substrate adhere torubber.

The invention also relates to such a substrate, notably made of steelsuch as a carbon steel. The steel may be bright (i.e. uncoated) or maybe at least partly coated with at least one layer (thus an intermediatelayer positioned between the steel and the polybenzoxazine layer) of asecond metal known as the surface metal, chosen from the groupconsisting of aluminium, copper, zinc and alloys of at least one ofthese metals with at least one other metal (belonging or not belongingto this group). This surface metal is in particular brass.

In order to adhere the rubber to the polybenzoxazine layer, use may bemade of any known adhesive system, for example a conventional textileadhesive of “RFL” type comprising at least one diene elastomer such asnatural rubber, or any equivalent adhesive known for impartingsatisfactory adhesion between rubber and conventional polymers such aspolyester or polyamide, for instance the adhesive compositions describedin patent applications WO 2013/017421, WO 2013/017422, WO 2013/017423,WO 2015/007641, and WO 2015/007642.

Before the above adhesive coating process, it may be advantageous toactivate the surface of the polymer of the invention, for examplephysically and/or chemically, to improve the adhesive uptake thereofand/or the final adhesion thereof to the rubber. A physical treatmentmay consist, for example, of a treatment by radiation such as anelectron beam, or by plasma; a chemical treatment may consist, forexample, of prior passage through a bath of epoxy resin and/orisocyanate compound.

A person skilled in the art will readily understand that the connectionbetween the metal substrate provided with its polybenzoxazine layer andthe rubber layer with which it is in contact will be definitivelyprovided during the final curing (crosslinking) of the rubber article inquestion.

6. EXAMPLES OF THE INVENTION

In the present patent application, unless expressly indicated otherwise,all the percentages (%) shown are mass percentages.

The following tests firstly describe the synthesis of two examples ofbenzoxazine compounds (Monomers M-5 and M-7), then that of apreferential polybenzoxazine (Polymer P-3) according to the invention,starting from the Monomer M-7. Lastly, adhesion tests are performed toillustrate the excellent adhesive performance of the polybenzoxazines ofinvention.

5.1. Synthesis of a Benzoxazine Sulfide (Monomer M-5)

For this synthesis, a 100-ml three-necked round-bottomed flask, equippedwith a thermometer, a nitrogen inlet, a magnetic stirrer and acondenser, is provided.

The synthesis is performed according to the procedure depicted in FIG. 7, as explained in detail below, starting with three compounds: aspecific ethylenically unsaturated phenol bearing a methoxyl group(compound 1; eugenol; Aldrich product E51791), paraformaldehyde(compound 2; Aldrich product 158127) and an aromatic diamine disulfide(compound 3; 3,5-bis(methylthio)-2,6-toluenediamine), in the presence oftwo solvents (anhydrous toluene and anhydrous ethanol).

Compound 3 was isolated, by chromatography on silica gel, from theproduct Ethacure 300 (supplier: Albemarle, Belgium), available in theform of a relatively viscous liquid of brownish colour; it is composedto approximately 96% of a mixture of3,5-bis(methylthio)-2,4-toluenediamine and3,5-bis(methylthio)-2,6-toluenediamine isomers (weight ratio ofapproximately 4/1 according to chromatographic analysis).

Compound 1 (2 eq., 4.93 g, i.e. 30 mmol) and then ethanol (51 ml) arepoured into the round-bottomed flask. The presence of ethanol isimportant in this instance, preventing the formation of an unstabletriazine-type intermediate product. Compound 3 (1 eq., 3.215 g, i.e. 15mmol), compound 2 (4 eq., 1.80 g, i.e. 60 mmol) and finally the toluene(102 ml) are subsequently introduced with stirring. The reaction mediumis heated (approximately 75° C.) at reflux for 4 h and, after distillingoff the ethanol at about 100° C. over 16 hours, the solvents andvolatile residues are then finally distilled off at 40° C. (under avacuum of 20 mbar) for evaporation. The final product is then washed(100 ml of methanol) and dried.

This powder is placed in methanol (50 ml per 4 g of powder) and themixture is heated at reflux (65° C.) for 30 min. The solution is thenleft to cool to room temperature (approximately 20° C.) forcrystallization of the monomer. The solid product obtained is isolatedby filtration (Büchner filter). After drying in a vacuum oven at 50° C.overnight, a powder is thus obtained, the ¹H NMR spectrum (500 MHz)(solvent: d8-THF) of which confirmed the chemical structure of theMonomer M-5 thus synthesized, with the following results:

2.07 (s, 3H), 2.38 (s, 6H), 3.25 (t, 4H), 3.71 (s, 6H), 3.94-4.01 (t,2H), 4.58-4.64 (dd, 2H), 4.81-4.86 (dd, 2H), 4.96-5.05 (m, 6H),5.85-5.97 (m, 2H), 6.37-6.40 (d, 2H), 6.55 (s, 2H), 6.72 (s, 1H).

5.2. Synthesis of a Halogenated Benzoxazine Sulfide (Monomer M-7)

For this synthesis, a 100-ml three-necked round-bottomed flask, equippedwith a thermometer, a nitrogen inlet, a magnetic stirrer and acondenser, is provided.

The synthesis is performed according to the procedure depicted in FIG.10 , as explained in detail below, starting with three compounds: ahalogenated phenol (compound 4; 4-bromophenol; Aldrich product B75808),p-formaldehyde (compound 2; Aldrich product 158127) and an aromaticdiamine disulfide (compound 3; 3,5-bis(methylthio)-2,6-toluenediamine),in the presence of two solvents (anhydrous toluene and anhydrousethanol).

Compound 3 was isolated, by chromatography on silica gel, from theproduct Ethacure 300 (supplier: Albemarle, Belgium), available in theform of a relatively viscous liquid of brownish colour; it is composedto approximately 96% of a mixture of3,5-bis(methylthio)-2,4-toluenediamine and3,5-bis(methylthio)-2,6-toluenediamine isomers (weight ratio ofapproximately 4/1 according to chromatographic analysis).

Compound 4 (2 eq., 2.6 g, i.e. 15 mmol) and then ethanol (23 ml) arepoured into the round-bottomed flask. The presence of ethanol isimportant in this instance, preventing the formation of an unstabletriazine-type intermediate product. Compound 3 (1 eq., 1.6 g, i.e. 7.5mmol), compound 2 (4 eq., 0.90 g, i.e. 30 mmol) and finally the toluene(46 ml) are subsequently introduced with stirring. The reaction mediumis heated (approximately 75° C.) at reflux for 16 h and then thesolvents and volatile residues are distilled off at 40° C. under vacuum(20 mbar) for evaporation.

The final product is then placed in methanol (50 ml per 4.5 g ofproduct) and the mixture is heated at reflux (65° C.) for 30 min. Thesolution is then left to cool to room temperature (approximately 20° C.)for crystallization of the monomer. The solid product obtained isisolated by filtration (Büchner filter). A yellow powder is thusobtained, after drying in a vacuum oven at 50° C. overnight (reactionyield equal to approximately 82%).

The ¹H NMR spectra (500 MHz) of the Monomer M-7 thus synthesized,dissolved in a deuterated solvent, confirmed its chemical structure,with the following results:

-   -   in d8-THF:

2.06 (s, 3H), 2.39 (s, 6H), 4.03-4.14 (t, 2H), 4.59-4.63 (d, 2H),4.87-4.91 (dd, 2H), 5.01-5.05 (dd, 2H), 6.71-6.74 (d, 2H), 6.81 (s, 1H),7.15-7.21 (m, 4H);

-   -   in CD₂Cl₂:

2.06 (s, 3H), 2.39 (s, 6H), 4.03-4.14 (t, 2H), 4.53-4.58 (dd, 2H),4.92-4.95 (dd, 2H), 5.00-5.04 (dd, 2H), 6.68 (s, 1H), 6.74-6.77 (d, 2H),7.14-7.15 (d, 2H), 7.21-7.24 (dd, 2H).

5.3. Synthesis of a Polybenzoxazine Polysulfide According to theInvention (Polymer P-3)

This synthesis is performed according to the procedure depicted in theFIG. 11 , as described in detail below, starting with two monomers: thebenzoxazine obtained in the preceding step (Monomer M-7) and thesulfur-bearing aromatic diol of formula (B-1) (4,4′-thiodiphenol;Monomer N-1); this being in the presence of sodium carbonate (Na₂CO₃;Sigma Aldrich product 13418), and the (anhydrous) solvents DMA(N,N-dimethylacetamide; Sigma Aldrich product 38839) and toluene (AcrosOrganics product No. 364411000). The two monomers (M-7 and N-1) aredried beforehand under vacuum (10 mbar) at 60° C. overnight, andlikewise for the sodium carbonate but at a temperature of 150° C.

The synthesis is performed in a 100-ml four-necked round-bottomed flask,equipped with a nitrogen inlet, a thermometer, a magnetic stirrer and aDean-Stark separator surmounted by a condenser and by a distillationbridge (provided with a heating mantle). The apparatus is dried undervacuum using a hot air gun until the thermometer reaches a temperatureof at least 100° C. in the reaction flask. The system is left to cool toroom temperature (20° C.) and the apparatus is then placed under astream of nitrogen throughout the synthesis.

First of all, the Monomer M-7 (1 eq., 1.5 g, i.e. 2.79 mmol) of formula(A-7) and then the Monomer N-1 of formula (B-1) (1 eq., 0.61 g, i.e.2.79 mmol) are then introduced into the round-bottomed flask. This isfollowed by addition of 20 ml of DMA (solvent of both monomers) andthen, as base, of Na₂CO₃ (3 eq., 0.89 g, i.e. 8.36 mol) suspended in 4ml of toluene. The system is purged under N₂ for 5 min and the reactionmedium is then heated to 105° C. Once this temperature is reached(heating mantle temperature of approximately 115° C.), the distillationbridge of the Dean-Stark apparatus is heated to 110° C. (with theheating mantle) in order to facilitate the azeotropic distillation(water/toluene distillation) performed for approximately 90 min. Thetemperature of the reaction medium is then gradually increased, instages of 10° C. every 30 min, until 130° C. is reached. The reactionmedium is left at this temperature for 17 h and is then left to cool toroom temperature (20° C.). The reaction mixture is subsequentlydistilled at 90° C. (vacuum 3 mbar) to remove the solvents and volatileresidues, and the solid precipitate thus obtained is then washed with250 ml of distilled water; during this washing, to extract thecarbonate, acid (1% aqueous HCl) is added dropwise until neutral pH isreached. The precipitate is once again washed with 100 ml of distilledwater and dried under vacuum at 80° C. overnight (approximately 12 h).

The Polymer P-3 of FIG. 11 was thus obtained, as attested to by the ¹HNMR analysis (500 MHz) in the solvent d8-THF, which gave the followingresults:

1.92 (s, 3H), 2.26 (s, 6H), 3.74-3.81 (m, 4H), 4.01-4.03 (t, 2H),4.75-5.01 (m, 2H), 6-15-6.75 (m, 4H), 6.90-7.45 (br, 11H).

This Polymer P-3, in the form of a pale yellow powder, was also analysedby DSC (Differential Scanning calorimetry) between −80° C. and +350° C.with a ramp of 10° C./min (Mettler Toledo DSC “822-2” machine; nitrogenatmosphere). The analysis showed, in the first pass (between −80° C. and+350° C.), an apparent glass transition (Tg) at 163° C. followed byexothermicity (corresponding to the opening of the oxazine rings and tothe crosslinking of the polymer) above 200° C., with two maxima atapproximately 270° C. and 299° C. During the second and third DSCpasses, performed between −80° C. and +350° C., no apparent glasstransition was visible.

5.4. Test of Adhesion in a Metal/Rubber Composite

A portion (325 mg) of the Polymer P-3 prepared above was dissolved in 8ml of DMPU (1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone; SigmaAldrich product 41661) with 10% by weight of “DY 9577 ES” accelerator(Huntsman product), this being in order to form a solution, a fraction(0.6 ml) of which was subsequently deposited uniformly on a brass tape(film) having dimensions of 10 cm×2.5 cm and a thickness of 0.5 mm; theassembly was placed in an oven at 175° C. (air ventilation) for 5 minand then for an additional 5 min at 230° C. under vacuum in order,firstly, to remove any trace of solvent and, secondly, to at leastpartially (that is to say, completely or partially) open the oxazinerings of the polymer, this last step being accompanied by a pronouncedchange in colour of the polymer, which changes to dark orange.

After cooling to room temperature, the tape provided at the surface withits thin (thickness 5 to 10 μm) layer of polybenzoxazine thus formed wassubsequently subjected to a conventional two-stage adhesive coatingoperation (two baths adhesive coating), first of all by immersion in afirst aqueous bath (approximately 94% water) based on epoxy resin(polyglycerol polyglycidyl ether, approximately 1%) and on isocyanatecompound (caprolactam-blocked isocyanate compound, approximately 5%),this first adhesive coating step being followed by drying (2 min at 100°C.) and then a heat treatment (5 min at 200° C.).

The tape thus treated was then immersed in a second aqueous bath of RFLadhesive (approximately 81% by weight of water) based on resorcinol(approximately 2%), on formaldehyde (approximately 1%) and on a rubberlatex (approximately 16% of NR, SBR and VP/SBR rubbers); finally, it wasdried in an oven at 130° C. for 2 min and then heat treated at 200° C.for 5 min.

The brass tape thus coated with the polybenzoxazine film and then coatedwith adhesive was subsequently placed between two layers of conventionalrubber composition for a belt reinforcement of a passenger vehicle tyre,this composition being based on natural rubber, on carbon black andsilica as filler and on a vulcanization system (sulfur and sulfenamideaccelerator); this composition was free of cobalt salt. The metal/rubbercomposite test specimen thus prepared was then placed under a press andthe whole was cured (vulcanized) at 150° C. for 30 min under a pressureof 20 bar.

After vulcanization of the rubber, excellent adhesive bonding betweenthe rubber matrix and the metal tape of the invention was obtained,despite the absence of cobalt salt in the rubber matrix; this isbecause, during peel tests (at 20° C.), it was found that the failureoccurred systematically in the rubber matrix itself and not at theinterphase between metal and rubber. Other adhesive bonding tests wereperformed on a bright (uncoated) steel tape; they also revealedexcellent adhesion to the rubber (systematic failure in the rubbermatrix).

In conclusion, the polybenzoxazine according to the invention offers themetal substrates the major advantage of being able subsequently to beadhesively bonded to rubber matrices using simple textile adhesives,such as RFL adhesives, or else directly (that is to say, withoutemploying such adhesives) to these rubber matrices, for example when thelatter contain appropriate functionalized unsaturated elastomers, suchas epoxidized elastomers. Thus, use may be made of metal substratesoptionally coated with adhesive metal layers such as brass, and alsosurrounding rubber matrices free of metal salts, in particular of cobaltsalts.

Moreover, this constituting a significant advantage compared to theother known polymers described in the introduction to the presentdocument, the polybenzoxazines of the invention have the noteworthyability, at high temperature, to open their oxazine rings and to thusgive a thermosetting polyphenolic resin structure. This gives thembetter heat stability. Finally, their specific microstructure makes itpossible, very advantageously, to adjust the flexibility of the moleculeaccording to the particular applications targeted.

The invention claimed is:
 1. A polybenzoxazine sulfide or ring-openedpolybenzoxazine sulfide, repeating units of which include at least oneunit corresponding to formula (I) or (II):

in which the a is an integer from 1 to 4, x is an integer from 1 to 8, Rrepresents hydrogen or a hydrocarbon-based group including 1 to 10carbon atoms and optionally a heteroatom chosen from O, S, N and P, and*, which may be identical or different, represents any attachment to acarbon atom or to a heteroatom chosen from O, S, N and P.
 2. Thepolybenzoxazine sulfide or ring-opened polybenzoxazine sulfide accordingclaim 1, wherein a is
 2. 3. The polybenzoxazine sulfide or ring-openedpolybenzoxazine sulfide according to claim 2, wherein the two groups offormula —S_(x)—R are in a meta-position relative to each other.
 4. Thepolybenzoxazine sulfide or ring-opened polybenzoxazine sulfide accordingto claim 1, wherein x is in a range from 1 to
 4. 5. The polybenzoxazinesulfide or ring-opened polybenzoxazine sulfide according to claim 1,wherein R is an alkyl containing from 1 to 5 carbon atoms.
 6. Thepolybenzoxazine sulfide or ring-opened polybenzoxazine sulfide accordingto claim 5, wherein R represents a methyl or an ethyl.
 7. Thepolybenzoxazine sulfide or ring-opened polybenzoxazine sulfide accordingto claim 4, wherein x is equal to 1 and R represents a methyl.
 8. Thepolybenzoxazine sulfide or ring-opened polybenzoxazine sulfide accordingto claim 1, the repeating units of which comprise at least one unitcorresponding to formulae (I-bis) or (II-bis):


9. The polybenzoxazine sulfide or ring-opened polybenzoxazine sulfideaccording to claim 8, the repeating units of which comprise at least oneunit corresponding to formulae (I-a) or (II-a):


10. A polybenzoxazine sulfide or ring-opened polybenzoxazine sulfide,repeating units of which comprise at least one unit corresponding toformulae (I-a-1), (I-b-1), (II-a-1) or (II-b-1):


11. The polybenzoxazine sulfide or ring-opened polybenzoxazine sulfideaccording to claim 1, the repeating units of which correspond to atleast one of formulae (I-1) or (II-1) below:

in which: X₁ and X₂, which may be identical or different, represent O orS; Ar₁ and Ar₂, which may be identical or different, represent anaromatic group; and Z represents O or (S)_(n), n representing an integergreater than or equal to
 1. 12. The polybenzoxazine sulfide orring-opened polybenzoxazine sulfide according to claim 11, the repeatingunits of which correspond to at least one of formulae (I-1bis) or(II-1bis) below:


13. A method for polymeric coating of a substrate, wherein at least asurface of the substrate is at least partly metallic, comprising thestep of: coating the substrate with the polybenzoxazine sulfide orring-opened polybenzoxazine sulfide according to claim 1 to form acoated substrate.
 14. The method according to claim 13, wherein thecoated substrate is bonded to a rubber.
 15. A substrate having at leasta surface which is at least partly metallic, the at least partlymetallic surface being coated with the polybenzoxazine sulfide orring-opened polybenzoxazine sulfide according to claim
 1. 16. Thesubstrate according to claim 15, wherein the substrate is made of steel.17. The substrate according to claim 16, wherein the steel is a brightsteel.
 18. The substrate according to claim 16, wherein the steel is atleast partially coated with at least one layer of a second surface metalselected from the group consisting of aluminum, copper, zinc and alloysthereof.
 19. The substrate according to claim 18, wherein the secondsurface metal is brass.